Abstract
AbstractWe present the analysis of global sympagic primary production (PP) from 300 years of pre-industrial and historical simulations of the E3SMv1.1-BGC model. The model includes a novel, eight-element sea ice biogeochemical component, MPAS-Seaice zbgc, which is resolved in three spatial dimensions and uses a vertical transport scheme based on internal brine dynamics. Modeled ice algal chlorophyll-a concentrations and column-integrated values are broadly consistent with observations, though chl-a profile fractions indicate that upper ice communities of the Southern Ocean are underestimated. Simulations of polar integrated sea ice PP support the lower bound in published estimates for both polar regions with mean Arctic values of 7.5 and 15.5 TgC/a in the Southern Ocean. However, comparisons of the polar climate state with observations, using a maximal bound for ice algal growth rates, suggest that the Arctic lower bound is a significant underestimation driven by biases in ocean surface nitrate, and that correction of these biases supports as much as 60.7 TgC/a of net Arctic PP. Simulated Southern Ocean sympagic PP is predominantly light-limited, and regional patterns, particularly in the coastal high production band, are found to be negatively correlated with snow thickness.
Highlights
Sea ice algae are a fundamental source of primary production (PP) for polar zooplankton, during the winter and early spring
We provide a general description of the E3SMv1.1-BGC configuration, MPAS-O BGC (Model for Prediction Across Scales – Ocean Biogeochemistry) and simulations used in the analysis
We focus on the 157-year constant-forcing simulation, analyze the ocean and sea ice state and suggest controls on net sea ice PP in the Arctic and Southern Ocean
Summary
Sea ice algae are a fundamental source of primary production (PP) for polar zooplankton, during the winter and early spring. Arctic sea ice algae favor the bottom 3–5 cm of the ice (Lee and others, 2008; Cota and others, 1991; Gradinger and others, 2012; Michel and others, 2002), while Southern Ocean ice algae thrive in freeboard and internal ice communities (Ackley and Sullivan, 1994; Meiners, 2013) These polar and regional differences are believed to derive from the sea ice physical micro- and macro-scale seasonal dynamics (Fritsen and others, 1994). We focus on the 157-year constant-forcing simulation, analyze the ocean and sea ice state and suggest controls on net sea ice PP in the Arctic and Southern Ocean For this analysis we define and map bounds for maximal sea ice algal growth from both observations and model output to better understand the constraints on ice algal production.
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